Studies of gluon TMDs and their evolution using quarkonium-pair production at the LHC
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Regular Article - Theoretical Physics
Studies of gluon TMDs and their evolution using quarkonium-pair production at the LHC Florent Scarpa1,2,a , Daniël Boer1, Miguel G. Echevarria3,4 , Jean-Philippe Lansberg2 , Cristian Pisano5 , Marc Schlegel6 1
Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands IJCLab, CNRS/IN2P3, Université Paris-Saclay, 91405 Orsay, France 3 Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, via Bassi 6, 27100 Pavia, Italy 4 Dpto. de Física y Matemáticas, Universidad de Alcalá, Ctra. Madrid-Barcelona Km. 33, 28805 Alcalá de Henares, Madrid, Spain 5 Dipartimento di Fisica, Università di Cagliari, INFN, Sezione di Cagliari, Cittadella Universitaria, 09042 Monserrato, CA, Italy 6 Department of Physics, New Mexico State University, Las Cruces, NM 88003, USA
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Received: 25 September 2019 / Accepted: 6 January 2020 / Published online: 4 February 2020 © The Author(s) 2020
Abstract J/ψ- or ϒ-pair production at the LHC are promising processes to study the gluon transverse momentum distributions (TMDs) which remain very poorly known. In this article, we improve on previous results by including the TMD evolution in the computation of the observables such as the pair-transverse-momentum spectrum and asymmetries arising from the linear polarization of gluons inside unpolarized protons. We show that the azimuthal asymmetries generated by the gluon polarization are reduced compared to the tree level case but are still of measurable size (in the 5–10% range). Such asymmetries should be measurable in the available data sets of J/ψ pairs and in the future data sets of the high-luminosity LHC for ϒ pairs.
1 Introduction The three-dimensional structure of the composite hadrons has widely been analyzed through the study of transversemomentum dependent parton distribution functions (TMDs) in the framework of TMD factorization. The various TMDs can be accessed in hadronic processes with a small transverse momentum (TM), denoted by qT , of the detected final state [1–3]. TMDs need to be extracted from experimental data for such processes as they are intrinsically nonperturbative objects and therefore cannot be computed using perturbative QCD. So far, the majority of data allowing for the extraction of TMDs have been acquired from SIDIS and Drell– Yan measurements, two experimentally accessible processes and for which TMD factorization was proved to hold [4– 6]. However, since such processes are primarily induced by a e-mail:
quarks/antiquarks, they mostly provide information about the quark TMDs. Currently our knowledge of gluon TMDs is still very limited, due to the lack of data on processes that could potentially be used for extractions. More specifically, gluons inside unpolarized protons can be described at leading twist using two TMDs [7]. The first one describes unpolarized gluons, while the second one describes linearly polarized gluons. The latter correlates the spin of the gluons with their TM, and thus requires non
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